A systems approach to bearing selection

In the SKF life rating equation, the stresses resulting from external loads are considered together with the tribological stresses in the rolling contact area. Understanding the influence of these combined stress systems on bearing life enables a more accurate prediction of how a bearing will perform in its application.

Due to its complexity, a detailed description of the theory is beyond the scope of this work. Therefore, a simplified approach is presented in SKF rating life. This enables users to fully exploit bearing life potential, to undertake controlled downsizing, and to recognize the influence of lubrication and contamination on bearing service life.

Bearing system life

Metal fatigue of the rolling contact surfaces is a well-known failure mode for rolling bearings. Metal fatigue can be the result of a variety of factors including but not limited to excessive frictional heat, poor or contaminated lubrication conditions, and heavy external and/or indeterminate loads.

Therefore, a criterion based on raceway fatigue is generally sufficient for the selection and sizing of a rolling bearing for a given application. International standards such as ISO 281:2007 are based on metal fatigue of the rolling contact surfaces. Nevertheless, it is important to remember that the complete bearing can be viewed as a system in which the life of each component, i.e. rolling elements, raceways, cage, lubricant and seals, when present, contributes equally and in some cases dictates the effective endurance of the bearing (fig. 1).

In various sections of this website, references are made to relevant aspects of the strength and suitability of other components of the bearing, viewed as a system, that need to be checked to attain the best performance.